With the large-scale deployment of 3G networks and the gradual deployment of 4G networks, the transmission rate of supported data terminals is getting higher and higher. The downlink data rate of 4G networks has reached 150MB/s or more. Therefore, the processing speed of terminal chips is increasing and the data is increasing. The increase of the processing rate also increases the pressure of the terminal power consumption. The interface of the main product form of the data card is the USB interface, and the maximum power consumption of the USB2.0 interface is limited to 5 V, 500 mA, which is difficult to meet the data card pair. Power requirements. In addition, the problem of heat generation due to the increase in power consumption seriously affects the user experience and the service life of the product. Therefore, low power design is necessary for product design of data cards.
1 Technical solutions for mainstream dual-mode data cards The dual-mode data card solutions currently on the market use two-standard terminal solution platforms. Because the products of the terminal platform chip manufacturers are focused, they will not support all. Technology platform, so Qualcomm has many CDMA-based data card terminal chips, but there is no WiMax terminal chip product. Therefore, it is necessary to integrate the platforms of various manufacturers to support the design of dual-mode card products. Because it is a platform to integrate different manufacturers, but also take into account the product development cycle, some hardware and software design may be ignored and the design is not optimal. The advantages and disadvantages of the two dual-mode data cards are analyzed below.
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1.1 Mainstream dual-mode data card solution 1
The technical advantages of the scheme are mainly that the integration of the two platforms is less difficult and the development cycle is shorter. The dual-mode data card on the market mostly adopts this scheme, but the scheme has obvious disadvantages.
(1) The switching between dual modes is slower, because the switching strategy should comprehensively consider the network information measured by the two platforms. There is no way to communicate between the two platforms, and it can only be sent to the host through the USB HUB. Software to control the switching between the two platforms.
(2) A HUB has been added, resulting in an increase in power consumption of the system by approximately 100 mA/5 V. For the power consumption of 500 mA/5 V required by USB2.0, the power consumption of many single-platform data card products is close to the upper limit of the power consumption data, so the increase of power consumption is already a big overhead, and at the same time Increased costs.
1.2 Mainstream dual-mode data card solution 2
The technical advantage of this solution is that it saves a HUB, reduces the cost, and the switching rate also increases, but the solution also has a disadvantage, that is, power consumption.
(1) Since the WiMax baseband chip and the EVDO baseband chip are not the same terminal chip manufacturer, the two modules will not be integrated in the processing performance, resulting in serious waste of CPU resources. When the WiMax system works, the CPU of the EVDO chip is To handle the packets sent from the SDIO chip, the EVDO baseband processor will also work, and the simultaneous operation of the two baseband processors will inevitably lead to an increase in power consumption.
(2) Due to the integration of the hardware and software resources of the two chips, it is necessary to coordinate the cooperation of the two terminal chip manufacturers, which will inevitably lead to the extension of the development cycle.
2 Proposed a low-power dual-mode data card technology solution Based on the above two solutions, a compromised technical solution is proposed, which reduces the overall hardware cost of the system while reducing the overall system cost. Power consumption increases switching time and shortens software development cycle.
The solution adds a USB Switch. The cost of the Switch is lower than that of the USB HUB, and its power consumption is negligible. This program has the following advantages:
(1) The power consumption of the USB Switch is negligible.
(2) The UART interface transmits some small amount of data control and status information, and does not involve high-level software modifications.
(3) Fast switching and low power mode.
2.1 Dual-mode dual-standby technology implementation process (1) Initial power-on is maintained by GPIO control USB Swithch to ensure communication between EVDO baseband chip and host, WiMax baseband chip does not communicate with the host but timing RF signal measurement, and through UART The signal is sent to the EVDO baseband chip.
(2) EVDO's baseband chip calculates which network serves the user according to a certain strategy.
1) If the service is provided by EVDO, WiMax enters standby mode, wakes up to perform network signal measurement, and sends network signal information to EVDO processor through UART. According to the strategy, if it is found that it needs to switch to WiMax network, EVDO is controlled by GPIO. The USBSwitch shuts down its communication with the host and communicates with the host via the WiMax baseband chip. The EVDO enters standby mode and wakes up periodically for signal measurements and passes the network signal to the WiMax baseband processor.
2) If the service is provided by WiMax, the EVDO controls the USB Switch to close the communication with the host through the GPIO, and the WiMax baseband chip communicates with the host. The EVDO enters standby mode and periodically measures the signal and passes the network signal to the WiMax baseband processor, and the WiMax baseband processor determines the network that serves the user based on the switching strategy. If you need to switch to EVDO, do the same.
2.2 Software and hardware technology feasibility analysis (1) hardware aspects.
The main obstacle in hardware is the time it takes for the USB communication channel to switch from the current platform to another platform. If the switching time is too long, it may affect the user's communication. When a switching event occurs, the USB data path is disconnected from the current platform to establish communication with another platform. When establishing communication, the communication platform is required to enumerate the device and the host to load the driver to the corresponding platform. The USB enumeration time and load drive time can be controlled at the ms level. Therefore, an increase in switching time is acceptable. The user's voice communication may have a delay during the switching time, but the impact is small. Due to the wide coverage of the WiMax network, it can reach 30 km in a wide area, so switching between user networks does not occur very often.
(2) Software aspects.
Compared with the scheme 1, the main workload to be added in the software is to transfer and exchange a small amount of network information through the UART (serial communication interface), and the information exchange can be completed by a simple underlying communication protocol. This function can be done at the driver level, and does not involve the modification of the high-level protocol software. Therefore, it is relatively easy to implement the function on the software, and it will not increase the development difficulty and cycle. The main work of the software is to coordinate the definition of two communication protocol information and UART driver modification by two platform vendors.
Dual-mode data card 3 Conclusion The new solution proposed in this paper, while reducing system cost, but also reduces power consumption, increases the user's experience, is an ideal dual-mode data card products solutions .
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